1. Field of the Invention
The invention relates to novel compounds, 2-arylnaphtho[1,8-bc]furan-5-ones (hereinafter, referred to as naphthofuranones) and photopolymerizable compositions containing naphthofuranones as a photopolymerization initiators for addition polymerizable ethylenically unsaturated compounds.
2. Description of the Prior Art
It is well known that when an unsaturated compound which can be hardened upon irradiation is used as the polymerizable component of a composition such as paint, a printing ink, an adhesive, etc., and such a composition is subject to the action of electromagnetic waves such as visible rays, ultraviolet rays, X-rays, etc., or particle rays such as electron rays, neutron rays, alpha rays, etc., the aforesaid component is hardened by polymerization and further when the composition is subjected to radiation in the presence of a photopolymerization initiator, the polymerization rate of the composition increases remarkably. These techniques are described in, for example, U.S. Pat. Nos. 3,551,235, 3,551,246, 3,551,311 and 3,558,387, Belgian Pat. No. 808,179 and Japanese Patent Application (OPI) No. 110,781/1974 (The term "OPI" as used herein refers to a "published unexamined Japanese patent application") (corresponding to U.S. patent application Ser. No. 328,442, filed Jan. 31, 1973) and now abandoned.
The hardened products obtained by such techniques possess such advantages as excellent flexibility, chemical resistance, abrasion resistance, luster, adhesive property but, on the other hand, they also possess such disadvantages as a low sensitivity, which means they require a long period of time for image exposure for the formation of images utilizing the composition. Therefore, problems arise such as in the case of delicate image exposure, images having good image quality cannot be reproduced if even the slightest vibration occurs in the operation. Furthermore, the irradiation energy of the light source or the particle ray source must be increased for exposure, which results in the deformation and deterioration of the layer of the composition by the large amount of heat which accompanies the increased irradiation energy. Also, compositions containing the aforesaid conventional hardenable ethylenically unsaturated compounds have the disadvantage that when the composition is provided with a comparatively high hardening response or sensitivity, the composition tends to harden during storage due to heat.